The present invention relates to a nonwoven fabric having a relatively low level of ionic contaminates which is achieved by exposing the fabric to a deionized water wash, preferably, in-line with the nonwoven production process, thereby eliminating, or at least reducing, the need for an expensive and time consuming cleanroom laundering. The fabric is primarily comprised of continuous filament fibers and may be manufactured into such end-use products as cleaning wipes and protective clothing for cleanrooms and surface coating operations, such as automotive paintrooms. Also encompassed within this invention is a method for producing a nonwoven fabric having a relatively low level of ionic contaminates.
Various types of fabrics have historically been manufactured into wiping cloths, or wipers, for utilization in a number of different cleaning applications, such as industrial cleanrooms, preparing surfaces for coatings, and general cleaning. Each different application emphasizes certain standards that these types of wipers should attain. For example, wipers utilized in cleanrooms must meet stringent performance standards. These standards are related to sorbency and contamination, including maximum allowable particulate, unspecified extractable matter and individual ionic contaminates. The standards for particulate contaminant release are especially rigorous and various methods have been devised to meet them. For example, U.S. Pat. No. 5,271,995 to Paley et al. describes a wiper having fused borders, the sealed edge of the wipers being present to reduce contamination caused by small fibers. U.S. Pat. No. 5,229,181 to Diaber, et al. describes a knit fabric tube, only two edges of which must be cut and sealed, thereby reducing the contamination caused by loose fibers from the edges. U.S. Pat. No. 5,271,995 to Paley et al. describes a wiper for a cleanroom environment that has reduced inorganic contaminants through the use of a specific yarn, namely “nylon bright.” U.S. Pat. No. 5,069,735 to Reynolds describes a procedure to cut the fabric into pieces using a hot air jet in the range of 600 to 800 degrees F. to melt the fibers, forming a sealed edge product with reduced loose fiber contamination.
Finishes to improve the sorbency of wipers made of hydrophilic fibers, such as polyester, have also been employed. For example, wiping cloths having a textile substrate and a porous polymer coating made from the “sulphonation products of cross-linked polymers containing sulphonated aromatic residues” are disclosed in GB 2 142 225 A.
Ions such as Na, Li, NH4, K, Mg, Ca, F, Cl, NO4, PO4, and SO4 are generally inherently present in a textile fabric. These ions may be detrimental to a cleanroom environment, especially in the semi-conductor industry, because the ions: (a) can be transferred to the silicon wafer circuitry; (b) can cause corrosion on the wafer circuitry, and (c) can cause short circuit in the wafer circuitry. It is known that deionized water may be used to reduce or eliminate these ions from the fabric so they may be suitable for use, for example, in cleanroom applications. Deionized water acts as an attractant to the ions in the fabric so that the ions are pulled oft the fabric and into the water, which can then be discarded or filtered for reuse. Typically, ion reduction or removal is achieved using a cleanroom laundry to wash the fabric, often in the form of wipers, to reduce ion content. However, this process is very expensive and time consuming and may detrimentally affect the physical properties of the fabric due to the conditions the wipers encounter during the wash cycle, such as overly aggressive agitation and rinsing and exposure to high temperature water and chemicals.
Wipers may be made from knitted, woven, or non-woven textile fabrics. The fabric is typically cut into 9-inch by 9-inch squares. If a wiper is intended for use in a cleanroom environment, it is generally desirable to wash the fabric or wipers in a cleanroom laundry in order to remove and minimize contamination of the wipers prior to packaging. The cleanroom laundry may employ special filters, surfactants, sequestrants, purified water, etc. to remove oils, reduce particle count, and extract undesirable ion contaminates. As mentioned previously, the laundering process, which is expensive and time consuming, may be overly aggressive and may detrimentally affect the physical properties of the fabric. For example, any finishes applied to the surface of the fabric may be removed during the laundering process and the fabric edges may become unraveled or frayed, thereby leading to an undesirable increase in fiber particle contamination. Thus, careful and constant monitoring of the laundering equipment employed is necessary in order control the agitation, volume and duration of rinsing, and speed and duration of extraction.
As interest in this industry has grown, manufacturers have worked to develop new yarns and fabrics that might easily and cost effectively fulfill this need for contaminant-free fabrics. One such advancement has been made in the area of spun-bonded nonwovens. Spun-bonded nonwoven production processes are well known in the textile arts and are described in various patents such as, for example, U.S. Pat. No. 4,692,618 to Dorschner, et al.; U.S. Pat. No. 4,340,563 to Appel, et al.; U.S. Pat. No. 3,338,992 to Kinney; U.S. Pat. No. 3,341,394 to Kinney; and U.S. Pat. No. 3,502,538 to Levy. Historically, the nonwoven webs produced from these processes have been produced for functional end-uses, such as for air filters, vehicle trunk linings, and roofing materials, with relatively low cost and little or no emphasis on characteristics such as drape and hand and moisture absorbency which are of considerable interest, for example, in cleanroom wiping cloths and protective clothing.
However, recent developments in the area of spun-bonded fiber production have resulted in the creation of nonwoven fabrics with improved drape, hand, and moisture absorption characteristics (“hand” typically describes the tactile qualities of a fabric such as softness, firmness, elasticity, etc.). For example, U.S. Pat. Nos. 5,899,785 and 5,970,583, both assigned to Firma Carl Freudenberg, describe a spun-bonded nonwoven lap of very fine continuous filament and the process for making such nonwoven lap using traditional spun-bonded nonwoven manufacturing techniques. Such references disclose, as important raw materials, spun-bonded composite, or multi-component, fibers that are longitudinally splittable by mechanical or chemical action into microdenier size individual fibers. However, while this nonwoven production process may be cheaper and simpler than a comparable knitted or woven process, the fabric produced therein would likely need to be processed at a cleanroom laundry to meet the requirements for end-use products, such as, for examples, wipers for a cleanroom or a paintroom.
Thus, an efficient, cost effective method is needed for achieving a nonwoven fabric having a relatively low level of particle contaminates and sufficient hand, drape, and moisture absorbency characteristics required for end uses such as cleanroom and paintroom wipers and protective clothing.